When using optical devices, for example, for ranging, guidance, communication or information gathering, such as binoculars, telescopes, periscopes, rifle scopes and the like, in daylight hours and particularly in sunlight, reflections of the sunlight can be readily observed. The observation of such reflections can be especially troublesome and even dangerous, for example, during warfare when such devices are being used in a battleground situation. Reflective flashes of light, for example, can alert enemy observers as to the location of personnel and/or equipment and permit fire, or other retaliating measures, to be directed at such locations.
Reflections may also be a problem at night, from moonlight or artificial light sources, as when night vision devices are being used by observers. Such reflections can also occur from other optically reflective surfaces, such as mirrors and headlamps on vehicles, and the like, to the detriment of field troops in the vicinity thereof. Such reflection problems have become even more serious lately for battlefield troops with the introduction of scanning laser beams used in locating and/or ranging devices, which beams can produce relatively high intensity and readily indentifiable reflections from glass or other mirror or mirror-like surfaces.
At present, the only practical solutions available have been to avoid using the optical devices in question, at least when the sun or other light source is in front of the reflective surface, or to cover up the reflective surfaces in some manner, or remove the optical devices or other reflective surfaces entirely, or to use an optical shade, or hood, adapted to fit on a device in much the same manner as a camera lens hood or shade is fitted to a camera lens.
An obvious disadvantage of the use of some of the above solutions is to eliminate or seriously reduce the information gathering capabilities of the field forces which depend upon such information to improve their effectiveness. Further, personnel may not remember, or be able, to remove, cover up, or otherwise neutralize or minimize the reflectiveness of the surfaces involved.
Moreover, many optical devices, such as binoculars, telescopes, and the like, have a relatively narrow field of view. Accordingly, the use of a standard-type lens shade having an aspect ratio that adequately corresponds to such narrow field of view so as to prevent undesired reflections is impractical since it results in a relatively long and extremely cumbersome lens shade. For example, for 10.times.50 binoculars, a suitable lens shade would be over two feet long, with even longer shades required for higher power devices. Such an approach becomes entirely impractical for most, if not all, situations.
Accordingly, it is highly desirable, if not necessary, to devise other techniques for substantially preventing reflections from the reflecting surfaces of optical or other devices due to the incidence thereon of sunlight, laser beams, or other light sources.